The present invention relates generally to connection devices, and, more particularly, to a bone connection device for rotational stabilization of bone segments.
Devices for the repair of large bone fractures (e.g., fractures of the femoral neck) have generally consisted of some combination of a lag screw with a side plate and some means for attaching these two components to one another and to the fractured bone segments. The ability to rotationally lock a lag screw (also known as a xe2x80x9chip screwxe2x80x9d) relative to its side plate is very important in such devices because rotational movement of the lag screw relative to the side plate following implantation can cause premature wear of the bone fragment and result in loosening of the system prior to complete healing.
Prior art devices have attempted to rotationally lock installed lag screws using keys, pins, rings, splines, etc. See e.g., U.S. Pat. Nos. 5,007,910 and 5,514,138 to Anapliotis, et al. and McCarthy, respectively. The additional operation time and tools required to align and properly install such equipment has fueled a desire for a simpler and more effective device for aligning and rotationally locking the lag screw relative to the side plate. Such a device would reduce surgical operation time and complexity and provide a more effective and efficient mechanism for rotationally locking a lag screw to its corresponding side platexe2x80x94an obvious benefit to both orthopaedic physicians and patients.
In a preferred embodiment, the present invention is a device for rotational stabilization of bone segments comprising: a bone lag screw having a bone-engagement end, a distal end, and a keyed cross-sectional profile, the bone-engagement end configured for engaging a first bone segment; a bone plate having a flat portion for engaging a second bone segment and a barrel portion having an internal bore for slidably receiving the lag screw; and a locking collar having a keyed internal profile that mates with the keyed cross-sectional profile of the lag screw to rotationally couple the locking collar and the lag screw when the lag screw is inserted through the locking collar, and an outer surface configured and dimensioned for (1) free rotation, in a first position, within the internal bore of the bone plate barrel portion and (2) frictionally engaging, in a second position, the internal bore of the bone plate barrel portion to resist or prevent rotation of the collar relative to the bone plate, and thereby resist or prevent rotation of the lag screw relative to the bone plate. The locking collar may be cylindrical, and the outer surface of the locking collar may be formed with a taper. The taper of the outer surface of the locking collar may range from about 0 degrees to about 10 degrees. The taper of the outer surface of the locking collar may be defined by a major diameter and a minor diameter, a distal end of the collar having the major diameter, and a proximal end of the collar having the minor diameter.
The internal bore of the bone plate barrel portion may also be formed with a taper and the taper of the outer surface of the locking collar may be of the same degree and profile as the taper of the internal bore of the bone plate barrel portion. In one specific example, an impact force on the distal end of the locking collar frictionally locks the tapered outer surface of the locking collar to the tapered inner surface of the bone plate internal bore, preventing further rotation of the collar relative to the bone plate, and thereby preventing further rotation of the lag screw relative to the bone plate. This frictional locking is known as the Morse Taper effect. The components described above (i.e., lag screw, bone plate, locking collar) may be formed of any bio-compatible material, but are preferably of stainless steel, titanium alloy, or titanium.
Alternatively, the outer surface of the locking collar may be formed with a reverse taper defined by a major diameter and a minor diameter, a proximal end of the collar having the major diameter, and a distal end of the collar having the minor diameter. The locking collar, in the second position, may then be frictionally engaged in a proximal section of the internal bore of the bone plate by a force in a distal direction (i.e., a force directed away from, rather than toward, the patient""s body), such as that applied with a slide-hammer.
The barrel portion of the bone plate may be angled relative to the flat portion, and the device may be configured and adapted for repair of fractures of the femoral neck (i.e., hip bone). It should be pointed out, however, that the device is generally applicable to any type of bone fracture where rotational stabilization is important. In addition, the locking collar may be formed with a plurality of partial lengthwise slots extending from a distal end of the collar toward the proximal end of the collar. The lag screw may be formed with a cancellous screw thread, or it may be formed with a plurality of helically twisted blades.
In one variation of this embodiment, the device may further comprise a threaded bore in the distal end of the lag screw, and a compression screw insertable into the threaded bore of the lag screw. When threaded into the threaded bore of the lag screw, the compression screw abuts a distal end of the locking collar and draws the lag screw in an axial direction to join the two bone segments and reduce the fracture. As with the elements discussed above, the compression screw may be formed of stainless steel, titanium alloy, or titanium.
In another embodiment, the invention is a device for rotational stabilization of bone segments comprising: a bone lag screw having a bone-engagement end and a distal end, the bone-engagement end configured for engaging a first bone segment; a bone plate having a flat portion for engaging a second bone segment and a barrel portion having an internal bore for slidably receiving the lag screw, part of the internal bore having a taper; and a cylindrical locking collar having a hollowed cylindrical interior, a keyed internal profile that mates with the keyed cross-sectional profile of the lag screw to rotationally couple the locking collar and the lag screw when the lag screw is inserted through the locking collar, and a tapered outer surface configured and dimensioned for (1) free rotation, in a first position, within the internal bore of the bone plate barrel portion and (2) frictionally engaging, in a second position, the internal bore of the bone plate barrel portion to resist or prevent rotation of the collar relative to the bone plate, and thereby resist or prevent rotation of the lag screw relative to the bone plate. An impact force on the distal end of the locking collar frictionally locks the tapered outer surface of the locking collar to the tapered inner surface of the bone plate internal bore, preventing further rotation of the collar relative to the bone plate, and thereby preventing further rotation of the lag screw relative to the bone plate. This frictional locking is known as the Morse Taper effect. The taper of the outer surface of the locking collar may range from about 0 degrees to about 10 degrees, and may be defined by a major diameter and a minor diameter, a distal end of the collar having the major diameter, and a proximal end of the collar having the minor diameter. The barrel portion of the bone plate may be angled relative to the flat portion, and the device may be configured and adapted for repair of fractures of the femoral neck (i.e., hip bone), but is generally applicable to any type of bone fracture where rotational stabilization is important. The components described above (i.e., lag screw, bone plate, locking collar) may be formed of any biocompatible material, but are preferably formed of stainless steel, titanium alloy, or titanium. In addition, the locking collar may be formed with a plurality of partial lengthwise slots extending from the distal end of the collar toward the proximal end of the collar. The taper of the outer surface of the locking collar may be of the same degree and profile as the taper of the internal bore of the angled barrel portion.
In an alternative arrangement, the outer surface of the locking collar may be formed with a reverse taper defined by a major diameter and a minor diameter, a proximal end of the collar having the major diameter, and a distal end of the collar having the minor diameter. The locking collar, in the second position, may then be frictionally engaged in a proximal section of the internal bore of the bone plate by a force in a distal direction (i.e., a force directed away from, rather than toward, the patient""s body), such as that applied with a slap-hammer.
The device may further comprise a threaded bore in the distal end of the lag screw, and a compression screw insertable into the threaded bore of the lag screw. When threaded into the threaded bore of the lag screw, the compression screw abuts the distal end of the locking collar and draws the lag screw in an axial direction to join the two bone segments and reduce the fracture. As with the elements discussed above, the compression screw may be formed of stainless steel, titanium alloy, or titanium.
In still another preferred embodiment, the invention provides an improved method for rotationally stabilizing bone segments utilizing a bone lag screw and a bone plate, the improvement comprising: sufficiently locking the bone screw to the bone plate by frictional engagement to rotationally stabilize the bone segments relative to one another. The method may further comprise: inserting a locking collar into a barrel portion of a bone plate; inserting a lag screw through the locking collar and barrel portion; rotationally coupling the locking collar and the lag screw; attaching the bone-engagement end of the lag screw to a first bone segment; and impacting the locking collar to frictionally engage an outer surface of the locking collar to the internal bore to resist or prevent further rotation of the collar relative to the bone plate, and thereby prevent further rotation of the lag screw relative to the bone plate.